Hydrofluorocarbon-based compositions are of interest for use as replacements for chlorofluorocarbon (“CFC”) and/or hydrochlorofluorocarbon (“HCFC”) compositions, which tend to be environmentally undesirable. In particular, applicants have recognized that compositions comprising mixtures of hydrofluorocarbon (“HFC”) and non-HFC fluids are of interest for use in a wide range of applications, including for use as propellants in aerosol or other sprayable compositions. Unfortunately, applicants have further identified a number of disadvantages associated with adapting typical HFC/non-HFC mixtures for use in aerosols.
One disadvantage associated with the use of typical HFC/non-HFC mixtures in aerosols is that different HFC/non-HFC mixtures, including those which comprise the same components but differ, even slightly, in the relative concentrations thereof, tend to form sprayable products having vastly different properties. For example, an important property of aerosols and other pressurized, sprayable products is the nature of the spray itself. Sprays may be characterized, for example, as “mists” versus “streams” or as “dry” versus “wet”. Although spray characteristics of an aerosol depend on several factors, one of the most important is pressure. It is well known in the art that changes in the pressure of an aerosol or other sprayable product can significantly alter spray properties. For example, higher pressures will generally yield more mist-like sprays while lower pressures will yield more stream-like sprays. The pressure of a typical aerosol is a function of the amount and type of propellant in the formulation and the amount and type of solvent or solvents in the formulation. The incorporation of a higher-boiling, hence lower-pressure, solvent into a formulation will tend to lower the pressure of the finished product while the incorporation of a lower-boiling, hence higher-pressure, solvent will tend to raise the pressure of the finished product.
Unfortunately, as is known in the art, HFC/non-HFC mixtures tend to undergo a significant change in boiling point for a relatively small change in the relative concentrations of the HFC/non-HFC constituents in the mixture. Consequently, slightly different HFC/non-HFC mixtures result in sprayable compositions having significantly different spray characteristics. Thus, even where one particular combination of two or more HFC/non-HFC solvents is deemed suitable for use in a given spray application, other combinations of the same two or more HFC/non-HFC solvents, which differ only slightly in the relative concentrations of the HFC/non-HFC solvents, may be unsuitable for the same application.
Applicants have come to appreciate that mixtures of two or more HFC and non-HFC solvents having relatively constant boiling points and vapor pressures—that is, boiling points and vapor pressures that change by a relatively small degree as the relative concentration of the mixture constituents changes—are desirable. In the manufacture of such mixtures, the relatively constant boiling point/vapor pressures would allow a wider range of compositions to be used for a given spray application. Unfortunately, HFC/non-HFC mixtures having such relatively constant boiling point and vapor pressure properties are not only uncommon, but also unpredictable.